"Their own statistics tell them that private prisons don't work yet they are so obsessed with privatisation that they cannot accept that it is time to dump their crazy plan."

Dr Richard Simpson said the SNP got it wrong

However, the executive was quick to dismiss the nationalists' claim as inaccurate.

Justice Minister Jim Wallace said Mr Swinney's conclusions were "simply bizarre" and that the private jail's performance was an example to other prisons in Scotland.

And his deputy, Dr Richard Simpson, said the SNP had misinterpreted the data.

He said: "If they (the SNP) had read the HM Inspectors' prisons report then they would have seen that Kilmarnock Prison has a number of pieces of best practice across the whole prisons' estate in Scotland.

"No prison is perfect but Kilmarnock is certainly not the worst."

The SNP in July said parliamentary answers suggested that the executive had tried to cover up subsidies to the prison.

Mr Swinney said at the time the subsidies amounted to £690,698, which was almost 70% of the estimated £1m profit made by Kilmarnock Prison Services in the past two years.

WATCH/LISTEN

ON THIS STORY

James Cook reports
"Kilmarnock Prison is Scotland's newest and according to the SNP - the worst"